This invention relates generally to apparatus and methods for detecting radiation, and more particularly to collimating probes and methods of their use for detecting, localizing, and imaging or mapping of radiation in biological systems or other system. Completeness of shielding of the radiation detector from all directions other than through the orifice of the collimator is significant in this invention.
The use of radioactive materials to tag tissue within a patient for effecting its localization and demarcation by radiation detecting devices has been disclosed in the medical literature for at least forty years. For example, in the 1949 Annals of Surgery, there appears an article entitled "The Clinical Use of Radioactive Phosphorous in Surgery and Brain Tumors", by Burtrum Selverstern, William Sweet, and Charles Robinson. That article discloses the use of Geiger Muller counters employed in the localization and demarcation of cerebral tumors.
Significant developments in the localization and demarcation of tissue bearing radioactive isotope tags for diagnostic and/or therapeutic purposes have occurred since that time. Thus, it is now becoming an established modality in the diagnosis and/or treatment of certain diseases, e.g., cancer, to introduce monoclonal antibodies tagged with a radioactive isotope (e.g., Iodine 131, Indium 111, Technetium 99m, etc.) into the body of the patient. Such monoclonal antibodies tend to seek out particular tissue, such as the cancerous tissue, so that the gamma radiation emitted by the isotope can be detected by some apparatus, e.g., Gamma Camera, to provide an image of the radiation emitting tissue.
As is known Gamma Camera imaging apparatus are extremely large, and thus not suitable for use in an operating room. Thus, while the surgeon may be able to utilize some hard copy image or data regarding the location of radioactively tagged tissue provided by Gamma Camera during the surgical procedure the surgeon will, nevertheless, want to manually explore various possible sites that may contain cancerous tissue to ensure that no such tissue has been overlooked or missed. Such action is typically accomplished visually and/or by palpation. Obviously, such inspection procedures are complicated by the limited amount of time available to the surgeon during the surgery, the type of cancer involved, and its possible location(s).
For example, to detect colon cancer the ability to manually pinpoint the location of the cancer is complicated by the fact that the abdominal cavity is bounded on the back by the peritoneum and behind that are the kidneys and the ureters and a significant number of lymph nodes. Surgeons are reluctant to enter the retroperitoneum unless they are reasonably sure that some cancerous tissue is there since entry into the retroperitoneum is fraught with peril of various complications. Nonetheless, there are significant chances that cancer-containing-lymph nodes which aren't big enough to be seen or felt are buried in the retroperitoneal fat. Complicating matters is the fact that the colon is surrounded by fat and the mesentery is surrounded by fat. All of the body structures that might contain tumor-involved-lymph nodes are also likely to contain significant amounts of fat. Therefore finding the tumor-containing lymph nodes among the fat is difficult. The Sigmoid Colon is mobile and can be found from the midline to the left lower abdomen, complicating tumor localization.
One type of apparatus which is small enough to be used in the operating room to assist the surgeon in detecting and localizing the presence of radioactively tagged tissue within the body of the patient makes use of a hand held radiation detecting probe consisting of a detector, shielding, and collimator. Such a probe is disposed or held adjacent to a portion of the patient's body usually exposed during surgical operations where the cancerous tissue is suspected to be in order to detect if any radiation is emanating from that site, thereby indicating that cancerous tissue is likely to be found there. Unfortunately, radiation from the tagged tissue scatters off of the various surrounding body tissue/organs, thereby rendering the localization of the source of the radiation difficult. More importantly, current radiolabelled monoclonal antibodies also localize non-selectively in liver and kidneys, providing intense background activity near tumor sites.
One technique for localizing the radiation source is to look for the highest energy rays emanated by the radioactive isotope. This technique is based on the theory that the lower energy rays received by the probe must have lost energy by scattering, whereas the higher energy rays remaining could not have undergone such scattering and must be coming in a direct line to the detector. While that technique has merit it does not deal with excluding all unscattered rays except those directly in front of the probe orifice.
An additional approach to localize the source of radiation is to utilize some shielding and collimating device with the detector so that the surgeon or operator of the device can adjust the solid angle (cone) in which radiation can be received or accepted by the probe's detector. One such probe and associated device is commercially available from Neoprobe Corporation under the designation Neoprobe 1000. That probe makes use of three collimators, each of which can be attached in either an extended or retracted position on the probe to establish a minimum and maximum solid angle from which radiation can be detected. In particular, each of the Neoprobe 1000's collimators is a device having a different size small diameter opening which is arranged when secured to the probe in the extended position (so that its narrow diameter provides a constrained or narrowed field, i.e., the minimum solid angle of acceptance) to localize the radiation source within a small area. When the collimator is retracted or removed the solid angle of acceptance is maximum, and thus the area from which the radioactivity can be detected is significantly larger. Thus, it is suggested that when using the Neoprobe 1000 that the collimator be removed or retracted for wide angle scanning (e.g., broad survey use), and that the collimator be connected and extended for localized scanning.
While such a probe may be generally suitable for its intended purposes, its use appears limited, i.e., it cannot provide optimum performance since it does not permit continuous varying of the solid angle of acceptance of the radiation, nor does it provide adequate shielding from the radiation entering from the back of the probe. In this connection it should be appreciated by those skilled in the art that the amount of radioactivity as well as the size and efficiency of the radiation detector within the probe and the solid angle of acceptance established by the probe's collimator determine the count rate. It has been determined that for a probe to be reliable on low count rates the counts in a suspected radioactive location should be at least two times the background level. Thus, in order to achieve optimal tradeoffs between the count rate, sensitivity and directionality, the probe must include some means for continuously varying the solid angle of acceptance of the radiation.
The following U.S. patents relate to collimators and/or apparatus for use with x-ray or other radiation detecting equipment, e.g., x-ray machines, etc: 3,112,402 (Okun et al.), 3,310,675 (Prickett et al.), 3,628,021 (MacDonald), 3,609,370 (Peyser), 3,869,615 (Hoover et al.), 3,919,519 (Stevens), 3,936,646 (Jonker), 4,340,818 (Barnes), 4,419,585 (Strauss et al.), 4,489,426 (Grass), 4,502,147 (Michaels) 4,782,840 (Martin Jr. et al.), and 4,801,803 (Denen et al.).